Analysis of impurity transport in both the melt and gas.
Prediction of oxygen and carbon containing species concentrations in Si CZ
growth. Adjustment of growth conditions and modification of the hot zone
aimed at providing desired impurity concentrations.

Automatic reconstruction of the geometry for
several crystal positions

Special models for anisotropic characteristics
of materials

The Basic CGSim program is developed for industries and research teams.
Graphical User Interface of the Basic CGSim code requires no special
computational skills. All setup and computational steps are highly automated
to minimize user efforts.

Work with Basic CGSim includes the following stages:

Specification of the growth system geometry

Specification of material properties

Grid generation

Boundary condition specification

Computation process

Visualization of the results

Below, we will have a closer look at some of these stages.

Geometry Specification

Fig. 2.
Specification of the Growth System in the Graphical User Interface
(GUI)

The Basic CGSim has a convenient tool for geometry specification. Any
geometry can be constructed by creating and manipulating geometric
entities, such as, points, lines, curves, etc. To facilitate the geometry
creation, the toolbox contains extensive set of tools for selecting,
moving, splitting, connecting, and duplicating objects as well as tools
for creating splines, polylines, and perpendiculars. If any modifications
are introduced into the complex multiblock geometry, the user only needs
to regenerate the grid and specify the materials in those blocks that were
modified, while the rest of the setup stays intact.

Advanced users familiar with AutoCAD can use it as an alternative geometry
specification tool and then import the geometry into CGSim using the DXF
format.

The CGSim code is a software designed specially for 2D axisymmetrical
computations, so the user only needs to create a half of the reactor
geometry.

Grid Generation

The built-in geometry analyzer automatically recognizes closed contours as
blocks, which substantially facilitates the geometry pre-treatment. This
feature is also very useful as a diagnostics tool—if some area of the
geometry, that stands for a separate construction element or a closed gas
volume is not recognized as a block, it means that the contour representing
its boundary is not closed. At the next step, the user can quickly generate a
grid for the whole system using the auto grid generator. Since the automatic
grid generator is very robust, the user only needs to set a parameter
characterizing desired grid refinement to start the grid generation. GUI also
provides the user with several options, facilitating the choice of blocks and
grid types for the automatic grid generation. For instance, the user can
choose the grid of some type to be generated in gas or solid blocks only.

Fig. 3.
Examples of grids generated by Basic CGSim

Advanced users can customize the mesh manually in selected blocks or
throughout the whole system. The grid generator supports triangular and
quadrangular grids with both matched and mismatched interfaces. These
capabilities are especially important for modeling of the crystallization
front geometry, when structured grids are required on both sides of the
interface. Local refinement of structured grids can be achieved through
refining the node distribution on the respective edges towards one of the
ends or symmetrically. For unstructured grids, refinement can also be
regulated through the grid quality parameters.

Materials

Fig. 4.
Assigning the Material Properties in GUI

The CGSim tool for setting characteristics of materials gives the user
wide possibilities. One can choose a constant, a polynomial function, a
piecewise linear function, expression, or an arbitrary function, which can be
programmed in the Function window. Plots for all characteristics can be
displayed in the same window. For example, the heat conductivity can be
defined as a function of temperature and coordinates in an arbitrary way
borrowed from literature. Incorporated programming language similar to
Pascal, extended by preprocessor and visualization of the function, allows
this for user.

After the geometry creation and the material specification, Basic CGSim
calculates the crystal and melt weights, and the initial charge weight,
which helps the user to draw crystallization zone geometry. Beside the
global heat computations with the given heater powers, Basic CGSim allows
searching the powers providing a certain crystallization rate and
prediction of crystallization front geometry.
The code permits automatic reconstruction of the geometry for several
crystal positions. To make it, the user has to build only the geometry with
the highest crystal position and to specify the crystal heights to be
computed.

CGSim View

Fig. 5.
1D and 2D Visualization with CGSim View

CGSim View allows analysis of 2D and 1D distributions including heat and
mass fluxes, V/G ratio and temperature gradient along the crystallization
front. Additionally, 1D distributions along a boundary can be displayed as a
plot and stored in a file on a hard disk. Built-in animation tools help to
analyze features of 3D melt convection.

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Platforms

The present version of basic CGSim operates under Windows 2000 and Windows XP.
The solver of Flow Module is available for parallel computations under Linux.